An optical transmitter-receiver (an optical transceiver) is an interface that is used in optical communications, and converts electricity into light. Conventionally, in an optical transceiver, an optical component having a box-type EML (Electro-absorption Modulated Laser diode) element is provided. Further, a board of the optical transceiver is connected to the EML element of the optical component via an FPC (flexible printed circuit board).
In such an optical transceiver, noise generated from the board is emitted to the inside of a housing from the FPC serving as a starting point, and hence it is necessary to suppress the emission of the noise to the outside.
In particular, in an optical transceiver that is compliant with 10GEPON having the transmission speed of 10 Gbps, noise of 10 GHz or higher is generated in the housing. As shown in FIG. 8, the noise of 10 GHz or higher passes through the housing (waveguide) of the optical transceiver without being attenuated, and hence the noise is easily emitted to the outside. Note that, FIG. 8 shows a transmission characteristic in the case where the noise is transmitted through the waveguide shown in FIG. 8 (the inner width a=6 mm, the inner height b=15 mm, and the total length L=100 mm).
Further, in the optical transceiver, an optical fiber is connected to an optical connector of the optical component, and each of the optical connector and a connection port of the optical fiber is composed of metal. In this case, when the optical fiber is connected to the optical connector, the metal of the optical connector and the metal of the connection port of the optical fiber function like an antenna. Thus, the optical transceiver unintentionally acquires a characteristic to emit noise to the outside.
On the other hand, in the optical transceiver, it is necessary to separate the ground on the side of the board (the signal ground) and the ground on the side of the housing (the frame ground) from each other because of specifications of the apparatus. On the contrary, in the box-type EML element used in conventional optical transceivers, its own ground is separated from the signal ground by providing a ceramic board in the connection portion with the FPC. With this, it is possible to separate the signal ground and the frame ground from each other.
In addition, in the optical transceiver that uses the box-type EML element, as countermeasures against the EMI, the optical component and the housing are physically (electrically) brought into direct contact with a conductive housing (see, e.g., Patent Document 1). Thus, by electrically grounding the optical component and the housing, it is possible to discharge noise from the FPC to the side of the housing to suppress the emission of the noise to the outside.